PG&E altering plans for Diablo Canyon offshore fault surveying

At the recommendation of a panel of state geologists, PG&E has modified its plans to conduct high-energy seismic surveys off Diablo Canyon nuclear power plant later this year.

The new plans shift the emphasis of the surveys south to San Luis Obispo Bay where the regionally dominant Hosgri Fault intersects the newly discovered Shoreline Fault. The duration of the surveys could also be cut back, which may reduce effects of the work on marine life.

The plan is under review by the state panel of scientists called the Independent Peer Review Panel, which includes county Supervisor Bruce Gibson, as well as the State Lands Commission, which is the permitting authority for the project.

These two groups agree the new plan is an improvement over the original and is likely to be the preferred alternative in an environmental impact report that is set to be published by the State Lands Commission later this month or in early March.

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“We told PG&E we think they are going over the right target areas,” said Gibson, who is a geophysicist. “In general, we think the footprint of the survey is covering the right geologic features.”

The survey work is scheduled to take place late this year and will consist of a large research vessel emitting blasts of very loud sound into the ocean as it sails in overlapping grid patterns. These sounds will penetrate deep into the Earth’s crust, echo back and be picked up by a large array of hydrophones towed behind the ship.

The resulting data will give seismologists a three-dimensional picture of the faults off Diablo Canyon and will allow them to more accurately assess the danger the faults pose to the nuclear plant. Completion of this work is a prerequisite for renewing the plant’s two operating licenses.

The surveys will cover a large swath of ocean from Cambria south nearly to Point Sal and will take an estimated 81 days of round-the-clock work to complete. The effect the loud sounds could have on sea life, particularly marine mammals, is the main environmental concern and will be the focus of the State Lands Commission review.

PG&E’s original plan called for a uniform area of ocean to be surveyed. The new plan narrows the overall width of the project but adds a new leg that focuses on the Shoreline Fault, as well as a new set of perpendicular surveys covering Estero Bay.

These changes potentially reduce the duration of the surveys by 10 percent. PG&E’s work estimates factor in extra time for unexpected stoppages, so further reductions in the project’s duration are possible, said Kris Vardas, PG&E environmental manager.

The new plan also significantly reduces the amount of surveying along the northern end of the Hosgri Fault, near the San Simeon Fault, an area seismologists believe they already understand well. The State Lands Commission’s environmental impact report may include an option for eliminating the northern leg of the surveys entirely, said Jearl Strickland, a PG&E manager of governmental affairs.

All of these changes have left the Lands Commission scrambling to meet its goal of publishing the environmental review within a month from now. The agency is doing the computer modeling needed to determine whether the 10 percent reduction in the number of survey routes, called race tracks, will actually lessen the impacts on marine mammals, said Cy Oggins, the commission’s chief of environmental planning.

“We feel strongly that we need to model these new race tracks,” he said. “It would have been nice to have these discussions last year rather than now.”

PG&E officials say their original proposal was a broad “placeholder” that was designed with a large enough footprint to cover the maximum environmental impacts. The plan could then be modified and even scaled back according to feedback from the peer review panel.

“It’s always easier to reduce the scope than increase the scope in an EIR,” Strickland said.

The Independent Peer Review Panel will continue its work and could recommend additional refinements, Gibson said. The five-member panel will hold another meeting Feb. 21.

One group that will definitely be affected by the survey work is commercial fishermen. They will not be able to fish in the survey area while work is under way.

PG&E is negotiating with the fishermen to come up with a plan to compensate them for income lost because of the project. The utility will also likely hire some fishing vessels to be used for marine mammal monitoring, Strickland said.

Once the environmental review of the project is published, a 45-day public comment period will open, which will include several local hearings. Final approval of the plan is expected in June at a certification hearing. Survey work would last from September to December.

The three-dimensional seismic surveys are the last segment in a three-part study to thoroughly assess the earthquake faults that surround Diablo Canyon. Lower-energy, two-dimensional offshore surveys as well as two-dimensional onshore surveys have already been completed.